Welder circuits



WELDER C IRCUITS Dec. 2s, 1943.

Filed Feb. 25, 1939 wlTNessEs; INVENTOR Josep/7 5/6/0/'0/7.

Patented Dec. 28, 1943 2,337,842 WELDER CIRCUITS Joseph Slepian, Pittsburgh, Pa., assigner to Westinghouse Electric & Manuf acturing Company,

East Pittsburgh, Pa., a corporation of Pennsylvania Application February 23, 1939, Serial No. 257,833

(Cl. Z50-27) 13 Claims.

My invention relates to electric discharge apparatus and has particular relation to the control of electric discharge devices.

The present invention is an improvement of the invention disclosed in issued on July 11, 1939.

In the said patent, a simple arrangement for controlling discharge valves of the ignitron type connected in anti-parallel, isdisclosed. The ignition electrodes of the valves are simply interconnected and the resultant current now -between the latter electrodes is suiicient to render one or the other of the valves conductive. To reduce the back current flow through the ignition electrodes of the ignitrons during their non-conductive half-periods, rectiers interconnect the ignition electrode and the cathode o each of the ignitrons, as shown in Fig. 2 of the copending application. The rectiers which are preferred in practice for this purpose are of the dry type and stacks of copper copper-oxide discs are ordinarily used.

While the arrangement is, in general, satisfactory, dinculties are encountered when the difference between the resistance of ignition'electrodes is' substantial. In such a case, the dry rectifier connected to the high resistance ignition electrode is heavily loaded when ignition current flows to the ignitron having the low resistance ignition electrode. Since in ordinary commy Patent 2,165,911,

be overheated by back current flow in spite of the fact that one of the electrodes has substantially greater resistance than the other.'

More generally stated, it is an object of my invention to provide an arrangement of simple structure for controlling a pair of ignitrons connected to conduct alternating half-cycles of current from an alternating-current source to a load in which a. Wide difierence in the conductivity of the ignition electrodes shall have no deleterious results.

According to my invention, the stacks interconnecting the cathodes and the ignition electrodes of the ignitrons comprise at least two rectifiers, and the ignition circuits are interconnected by conductively connecting points between the rectiers of each stack. The resultant connection is such `that when ignition current flows mercial work it is diilcult to select the igntrons y so that they have ignition electrodes of the same resistance, the possibility oi overloading the rectiiiers must be anticipated, and rectiers of higher rating than-would otherwise be necessary must be used.

Moreover, the forward resistance of the rectiers is appreciable and, therefore, when current ows through the low resistance ignition electrode, an appreciable potential drop exists across the high reactance electrode. In an arrangement in'which the resistances of the ignition elec.. trodes are unbalanced, the high resistance ignition electrode is. therefore, overheated by the back current flow.

It is accordingly an object of my invention to provide a control arrangement of the type disclosed in the said patent, in which overheating of the rectiers connected between the ignition electrodes and the cathodes shall not occur in spite of any existing difference in the resistance between the ignition electrodes.

Another object of my invention is to provide an arrangement such as is disclosed in the said patent in which the ignition electrodes shall not through the circuit, a, conductive rectifier from one stack is connected in parallel and another non-conductive rectifier from the same stack is connected in series with the ignition electrode of the valve that is at any time to be non-conductive, and a conductive rectiergfrom the other stack is connected in series and a. non-conductive rectier from the latter stack in parallel with the valve that is to be conductive. Hence, regardless of the direction of the current flow through the yignition circuit, the ignition current is at all times carried by parts of both of the stacks of rectiflers. and the stacks are, therefore, uniformly loaded. Moreover, because a nonconductive rectiiier is in series with the ignition electrode through which the back eurent flows, the magnitude of the latter current is substanmany reduced and the ignition electrode is not overheated.

It is to be noted that, while the uniform loading of the rectiiiers is, to a certain extent, tied up with the use of stacks of dry rectifiers, the excessive heating of the ignition electrodes is suppressed in an arrangement in which rectiflers of the ordinary discharge type are utilized. Accordingly, apparatus in which discharge rectifiers are connected between the ignition ele'ctrodes and the cathodes of ignitrons in the same manner as the dry rectifiers discussed above, is Within the scope of my invention. Of course, the dry rectiiiers may also be replaced by electrolytic rectiflers.

Moreover, it is to be noted that while my invention is principally applicable to the case in which ignitrons are connected in anti-parallel between the source and the load, it may also be used in other arrangements. For example, a

single ignitron may be connected between the source and load, and the ignition electrode may be connected to one terminal of the source or to an independent alternating-current source through the rectifier arrangement disclosed herein, My invention is also applicable Where the ignitrons are connected to conduct full-Wave direct current rather than alternating current from the source.

The novel features that l consider characteristie oi my invention are set forth with particularity in the appended claims. The invention 1tself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the drawing, in which the single figure is a diagrammatic view showing a preferred embodiment of my invention.

Specincally, my invention is shown herein as applied to supply current to a spot welding system. The apparatus comprises a welding trans former across the secondary 3 of which a pair of welding electrodes 5 are connected. The electrodes engage a material 'l to be welded, and when the transformer is energized, current ows through the material.

' The primary 3 of the transformer i is supplied from an alternating-current source il, which may be oi the usual commercial GO-cycles type through a pair of ignitrons i3 and l5 connected in anti-parallel. Each of the ignitrons has an anode Il, a mercury pool cathode |53, and an ignition electrode 2i. Between the cathodes I9 and the ignition electrodes 2l of the ignitrons i3 and |5, stacks 23 and 25 respectively, of dry rectiiiers are connected. The stacks 23 and 25 are conductive to current flow from their associated eathodes i3 to the corresponding ignition electrodes 2|, as indicated by the arrows, i. e., to electron iiow from the ignition electrodes to the cathodes. Points 2l and 2Q intermediate the ends of each of the stacks 23 and 25 are interconnected for a predetermined interval of time and when this occurs, current flows alternately through the ignitrons i3 and l5 and the material is welded.

assegna cycle of current is conducted through the ma To initiate a welding operation, a circuit controller 3|, which may be a push button or a loot switch, is operated, and its upper contacter 33 interconnects the conductors 35 and 3l from the intermediate points 2l and 29 of the rectier stacks 23 and 25, When the controller 3| is operated, the source has a certain polarity. To explain the operation, we may assume that the circuit controller is closed when the upper line conductor 39 is positive and the lower line conductor 4| is negative. l' In this case, current iiows in a circuit extending from the upper line oonductor 39 through a conductor 43, the lower portion 45 of the rectifier stack 25 in the ignition circuit of the right-hand valve |5, the conductor 31, the contacter 33 of the circuit controller 3i, the conductor 35, the normally closed contacts 41 and 49 of a timing relay 5|, a conductor 53, the upper portion of the rectifier stack 23 in the ignition circuit of the left-hand valve I3, the ignition electrode 2|, and cathode i9 of the lefthand valve, the primary 9 of the welding transformer l, a conductor 5l to the lower line conductor 4| of the source. The left-hand valve I3 is rendered conductive by the current flow through its ignition electrode and cathode, and a halfterial 'l to be welded.

During the succeeding half-cycles, ignition our rent for the right-hand valve i5 first ilows in a circuit extending from the lower line conductor1 4| of the source li, through the conductor 5l', the primary 9 of the Welding transformer l, the lower portion 59 of the left-hand rectifier stack 23, the conductor 53, the contacts 4l' and 49 of the timing relay 5|, the conductor 35, the upper contactor-33 of the circuit controller 3|, the conductor 3l, the upper portion 5| of the right-hand rectifier stack 25, the ignition electrode 2i and cathode I9 of the right-hand ignitron I5, the conductor 43 to the upper line conductor 33 of the source Ii. Now the right-hand ignitron i5 "is rendered conductive and a half-cycle of current of opposite polarity is conducted through the material l.

It is to be noted that in each case, the back current flow through the cathode l5 and the ignition electrode 2i of the ignitron i5 or I3 that is not to conduct current, is materially decreased by the portion of the rectier 6i and 55 respectively, in series with the ignition electrode. Moreover, where there is substantial dierence in the conductivity of the two ignition electrodes 2|, the rectifier stacks 23 and 25 will be heated uniformly, since the ignition current for the low resistance electrode i9 flows through a portion 55 or 6l of the rectifier 23 or 25 associated with the high resistance electrode IS, as well as through a portion 5t or L15 of its associated rectifier, and a portion of the substantially smaller current which ows through the high resistance ignition electrodc i5 also flows through a portion El or 55 of the rectier stack associated with the low resistance ignition electrode, as well as through a portion 45 or 59 of its associated rectifier. For example, if the ignition electrode i9 of the valve i3 has a higher resistance than the electrode t9 of valve l5, the uniform heating is attained because the high ignition current for valve |5 flows through the portion 59 of the stack 23 and the portion (il of stack 25, and the low ignition cur-- rent for valve |3 flows through the portion 45 of stack 25 and the portion 55 of stack 23.

The ignitrons i3 and l5 continue to conduct during alternate half-cycles of the source for an interval of time predetermined by the timing relay 5l. The circuit controller 3| is provided with a normally closed contacter 53 which short circuits the exciting coil 55 or" the timing relay. When the controller 3i is operated, the short circuit is raised and when, immediately thereafter, the welding transiormer'l is energized, a potential is impressed across the operating coil t5 of the timing relay, and the latter is energized and gradually raises an operating lever El. After an interval of time, predetermined by a cam 69 cooperating with the lever El, the lever engages a leaf spring '1| supporting one of the closed movable contacts 4l of the timing relay and disengaging it from the other contact 49, and opening the ignition circuits of the valves i3 and l5. After the contacts 47 and 43 are disengaged the lever 61 causes another pair of contacts 73 and 'I5 to become engaged. A circuit is closed which extends from the upper line conductor 39 of the source through the conductor 43, a resistor ll, the contacts 13 and 75 of the timing relay 5|, .a conductor 79, a resistor 8l, the exciting coil '65 of the timing relay 5|, a conductor 83, the conductor 57, to the lower line conductor 4| of the source 'lhe operating coil 63 of the timing relay ll is thus locked in and prevents further ignition ci the valves until the system is reset by releasing the circuit controller 3l and short circuiting the operating coil. Of course, the circuit controller 3l may be mechanically or electrically interlocked with the welding electrodes l or the mechanism which moves the material 1 to be welded, sothat a series of spot welds are produced by the successive operation of the controller Il.

It is to be noted that as the stacks 23 and 25, in general, include more than two rectiiier discs, a number of points of interconnection may be selected. For example, where each stack has three rectiers, the points may be selected so that one rectifier of each stack is in parallel with the ignition electrode and two are in series, or vice versa. The connection may also be asymmetric, that is, at one ignitron, one rectier may be in parallel with the ignition electrode and two` in series, while at the other ignitron. two may be in parallel and onein series. The character of the connections which are in any case selected depends on the properties of the ignitron used.`

The resistances of ignition electrodes may have as great a ratio as 5 to 1 and the connection of the rectifier may be selected so that the operation is most propitious.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention: f

l. In combination, an ignitron having a cathode and an ignition electrode, means interconnecting said cathode and said ignition electrode and including a stack of dry rectiers connected to conduct current from said cathode to said ignition electrode, current conducting means for supplying ignition current to said ignition electrode connected to a point intermediate the ends of said stack and said cathode and means for supplying current to said conducting means.

2. In combination, with a source of alternating current a first ignitron having an anode, a cathode and an ignition electrode, a second ignitron having an anode, a cathode and an ignition electrode which may differ substantially in conductivity from the ignition electrode of. said first ignitron, means for connecting the anode of said first ignitron and the cathode of said second ignitron to one terminal of said source, means for connecting the cathode of the rst ignitron and the anode of said second ignitron to the other terminal of said source, means interconnecting the cathode and the ignition electrode of said rst ignitron including a first stackv of dry rectifiers connected to conduct current fromthe said cathode to the said ignition electrode, means interconnecting the cathode and the ignition electrode of said second ignitron including a second stack of dry rectiers connected to conduct current from the said cathode to the said ignition electrode and current conducting means interconnecting a point intermediate the ends of the ilrst stack of dry rectiiiers and a point intermediate the ends of the second stack of dry rectiers, whereby the stacks of rectiilers are uniformly heated in spite of any diierence in the conductivity of said ignition electrodes.

3. For use in supplying current from a source oi alternating current to a load the combination comprising a pair of ignitrons interposed between said source and said load in such manner as to conduct alternate haii-cycles of-current from said of alternating current to a load the combination comprising a pair of ignitrons interposed between said source and said load in such manner as to conduct alternate half-cycles of current from said source to said load, each of said ignitrons having a cathode and an ignition electrode, a

stack of dry rectiers interposed between each ignition electrode and the corresponding cathode in such a sense as to conduct current'irom the control electrode to the cathode and means for conductiveiy interconnecting points intermediate the ends of said stacks for a predetermined interval of time.

5. For use in supplying current from a source o alternating current to a load the combination comprising a pair of ignitrons connected in antiparallel between said source and said load, each of said ignitrons having a cathode and an ignition electrode, a stack of dry rectiers interposed between each ignition electrode and the corresponding cathode in such a sense as to conduct current from the control electrode to the cathode and means for conductiveiy interconnecting points intermediate the ends of said stacks for a predetermined interval of time.

6. For use in supplyimg current from a source of alternating current to a load the combination 40 comprising a pair of electric discharge devices interposed between said source and said load in such manner as to conduct alternate half-cycles of current from said source to said load, each oi 'said electric discharge devices having a cathode and a control electrode, a plurality of rectiilers interposed between each control electrode and the corresponding cathode in such a sense as to conduct current from the cathode to the control electrode and means for conductiveiy interconnecting points between the rectifiers of each said plurality of rectiers.

7. In combinationl an alternating current supply circuit, a load circuit, electric translating apparatus connected between said circuits and comprising a pair of reversely connected electric valve means each having an anode, a cathode and a control member, a control circuit connected across the control members, and timing means connected in said control circuit and including means for conducting current between said control members for effecting energization of said load circuit for a predetermined interval of time.

8. In combination, an alternating current supply circuit, a load circuit, electric translating apparatus connected between said circuits and comprising a pair of reversely connected electric valve means each having an anode, a cathode and a control member of the immersion-ignitor type. a control circuit connected across the immersionignitor control members and including means for conducting current between the control members, and means connected in said control circuit for 75 .selectively opening and closing the control circuit to control the energization of said control members.

9. In combination, an alternating current supply circuit, a load circuit, electric translating apparatus connected between said circuits and comprising a pair of reversely connected electric valve means each having an anode, a cathode and a control member of the immersion-ignitor type, a control circuit connected across the immersion-ignitor control members and including means connecting said control members in series with each other in said control circuit so as to conduct current from one of said control members to the other, and means connected in said control circuit for selectively opening and closing the control circuit to control the energization of said control members.

10. In combination, an alternating current supply circuit, a load circuit, electric translating apparatus connected between said circuits and comprising a pair of reversely connected electric valve means each having an anode, a cathode and a control member, a control circuit connected across the control members, a pair of vunidirectional conducting devices each associated with a different one of said electric valve means and each being connected between said control circuit ancl the cathode of the associated electric valve means and being poled to transmit current from saidA supply circuit through said control circuit to the control member of the other electric valve means, and timing means connected in said control circuit for effecting energization of said load circuit for a predetermined interval of time.

1l. For use in supplying current from a, source of alternating current to a load the combination comprising a pair of ignitrons interposed between said source and said load in such manner as to conduct alternate half-cycles of current from said source to said load. each of said ignitrons having a cathode and an ignition electrode, said ignition electrodes at times diering substantially in conductivity, a stack of dry rectlilers interposed between each ignition electrode and the corresponding'cathode in such a sense as to conduct current from the control electrode to the cathode and means for conductively interconnecting points intermediate the ends of said stacks for a predetermined interval of time, whereby said stacks are uniformly heated by current iiow therethrough in spite of diiIerences in the conductivity of said ignition electrodes.

12. For use in supplying current from a source of alternating current to a load the combination comprising Aa pair of ignitrons connected in anti-parallel between said source and said load, each of said ignitrons having a cathode and an ignition electrode, said ignition electrodes at times diiering substantially in conductivity, a stack of dry rectiflers interposed between each ignition electrode and the corresponding cathode insuch a sense as to conduct current from the control electrode to the cathode and means for conductively interconnecting points intermediate the ends of said stacks for a predetermined interval of time, whereby s aid stacks are uniformly heated by current iiow therethrough in spite of differences in the conductivity of said ignition electrodes.

13. For use in supplying current from a source of alternating current to a load the combination comprising a pair of electric discharge devices interposed between said source and said load in such manner as to conduct alternate half-cycles of current from said source to said load, said devices conducting the load current, each of said electric discharge devices having a cathode and a control electrode, a plurality of rectiilers interposed between each control electrode and the corresponding cathode in such a sense as to conduct current from the cathode to the control electrode and means for conductively interconnecting points between the rectiers of each said plurality of rectiiers.

JOSEPH SLEPIAN. 

